Tunnel kiln



Parenteel oef. 28, 1930` UNITED: STATES par ARTHUR MCDOUGALL DUCKHAM'Q oF .LonDomnNGLAnn TUNNEL Kinn Y, Application filed July 16,1928, Serial No. 293,683,1al1id GreatBritainugstiZ, 11,927-, J

This invention relates to recuperative annular mui'ile kilns of the kind in which the,

goods are moved through the kiln on a circular track and pass successively through a preheating zone, a zone of open firing wherein they are fired by direct contact with hot combustion gases introduced into the interior of the kiln chamber, and a cooling zone, and wherein thehot combustion gases are ,.j withdrawn from the zone of open firing into ferred to, the suction or pull of the chimney Y the goods to be fired.

iiues arranged in the walls of the preheating zone, where they serverto preheat indirectly In known kilns of the character just restack or fan `acts only on the zone of open firing, the intention being that the atmosphere in the cooling and preheating zones shall be substantially quiescent. In practice, how- '20 ever, convectioncurrents' are set up in the atmosphere in the cooler parts ofthe kiln in such a way that the atmosphere in the cooling zone moves along more or less circular paths in the direction away fromy .theV cooler parts 2 of the Zone towards the firing zone. These V convection currents not only dissipate heat from the hottest portion ofthe kiln, but also tend to interfere with the proper cooling of the goods leaving the kiln. The intensity of such currents is enhanced by the presence of any air which may have filtered into the kiln. In my application for U. S. atent, Serial No. 182,148, filed April 8, 192 ,I have described a kiln of the aforesaid character wherein the portion of the kiln constituting the cooling zone is connected by a duct with the main waste gas flue for kthe purpose of minimizing convection currents apt to be set up in this zone. l

Ther present invention improves the lconstruction of the kiln in two respects, 'both connected with the rate of change of the temperature of the goods in their passage through the kiln.

On the cooling side'of the zone of open heating, the formationof convection currents is minimized by connecting the exhaustduct or ducts with longitudinal iiues in the walls of cooling zone which is betweenlthersaid or'dfucts and the zone of'wopenheating.

The advantagelof this construction is that f the goods-leaving `the zone ofopenheating arefmore gradually cooled than they .are 'when the longitudinal iiues inthe walls of the cooling zone of the kiln are usedwholly for 'conveying secondary air for combustion, as in known constructions.

f On the left the said zone escape throughports at the lower part'of the muiile Vcha,mber,and accord. ing to a further feature of the present invenly tion, the ports are grouped and those ofeach preheating side ofthe zoneV of. openY heating,the products of combustion that have group communicate with a separate ductfin the 'lower part ofr the kiln wall, whichductin turn, communicates under control With-the Ywaste Vgas "flues in -the walls' of4 the kiln. In

this manner the combustion products can be caused to pass among ,theV goods to be pree heated for as great a. distancey through the muflieV as may beirequired with due regard Yto the nature of the goods and their sensitiveness to the detrimentalefl'ect of` combustion gases.

The invention will be betterflinderstood by referring `to the accompanying drawings,`in Whicht-i f f i A F ig; l is a developed longitudinal section through the cooling zone', the zone of open heating and .thepreheating zone ofvan annue larkiln.' j Fig. 2 is a developed-sectional plan.

Fig. Sisa cross section on line 3.-?) of Fig. land"k f f Fig. 4 is a crosssection on line H'of Figil-L, Y *The travel the zone yof open h'eatingeand the cooling zone a number of verticallyA aligned ports' a Aconnect verticalnflues ib with the interior of the of -thefgeede ie 1in-the direetfie of the arrow inFig. '2. Near the junction of kiln, andzhorizontal fines c inthe-walls of the'.` i

kiln connectthe :verticalfiues @with like flues (Z towardsthe other end ofthe cooling zone.- kThe last-named iiues are connected by ghe exhaust ducts e with the main waste gas ue. f The remainder of the cooling zone has horizontalflues f. in its-walls for `secondary air,

" Litmanen,W

which, at the place where the fines d are situated is carried by ascending lues g into the horizontal flue h (Fig. 3) in the roof of the kiln and so to the combustion flues.

The result is that the first part of the cooling zone in the direction of travel is laterally protectedfrom ra id radiation by a more or less quicent or ow moving mass of combustion products in the lateral flues; a too rapid cooling of the goods is thus avoided; and the connection of the interior of the kiln chamber with the waste gas flue (by way of the ports a, fines b, c and d, and ducts e) has the eectof minimizing convection currents in the cooling zone. A

V,In the preheating zone there vare ducts i at the lower party of ythe walls and these ducts communicate with the interior of the kiln through the ports lc. At the ports lc the ducts communicate with the fines Z in the walls of the kiln, the communication being controlledby dampers m. It will be seen that if the dampers m of the first duct, namely, that next to the zone of open heating n be closed, the whole of the products of combustion will have to travel in the muiile chamber as far as the secondduct and so on. o is the ue connecting fines l with the chimney stack.

Having thus described the nature ,of the slid invention and the best means I know of carrying the same into practical effect, I dnn-.-

1. .In an annular tunnel kiln of the kind herein referred to, longitudinal flues ar'- rangedrin the walls of the cooling zone of the kiln, and an exhaust duct in communication with the said ylues and with the waste gas ue, said flues having communication with the interior of the kiln chamber intermediatel `.of the said duct and the zone of lopen l21.*gln an annular tunnel kiln of the kind herein referred.k to, longitudinal lues arranged in the walls of the cooling zone, an exhaust duct in communication with said flues and with the waste gas flue, said flues communicating-with the interior of the kiln chamber intermediately of the said yduct and the zone of open firing, flues arranged in the walls df thepreheating zone, and means forv withdrawing combustion gases from the zone of openfirinig into the last-named lues, said 'means comprising a number of ports arranged in groups, anda duct for each group communicating with the ports of that group, and in controlled communication with the fines in the walls of the preheating zone. 3. In anannular tunnel kiln of the kind herein reerred to, having iuesy arranged in the Halls of the mpreheating zone, means for `ufiishidrsnlvin'g co ustion gasy from the zone of open firing into said lues, said means comrising a number of orts arranged in groups and aV duct for eae group communicating with the ports of that grou trolled communication with t 'and in cone flues 1n the walls of the preheating zone.

have signed my UGALL DUCKHAM. 

